What is the distance across our solar system in light years?
Assuming that the heliosphere (solar-system sphere) is of radius Sedna's mean distance 100 AU, the solar system across is at least 0.0032 ly wide.
1 ly = 62900 AU, nearly.
It is discoveries galore in this 21st century. Sedna might have aphelion near 1000 AU. Planet X detected at about 200 AU, Some comets seem to have much longer periods. So, if the radius of heliosphere is changed to 1000 AU, the answer will be 0.032 ly.
A Mon Avis: The nearest star is about 4.2 ly away. So, the demarcation in-between might be imagined at about 2 ly. This is a point to ponder.